How big is the fallout from Andre Roberson’s injury for the Oklahoma City Thunder?

Roberson went down in a scary-looking fall during the third quarter of Oklahoma City’s win Saturday in Detroit, and the team announced Sunday that a ruptured patella tendon will end his 2017-18 campaign.

He’s the best perimeter defender on a team that — despite its star power — has won more with defense than offense this season. Just how much impact will losing him have on the Thunder’s chance of advancing deep in the playoffs? That answer might depend on how Oklahoma City goes about filling in for him.

Roberson’s defensive value

A number of statistics point to Roberson’s value at the defensive end of the court. According to NBA Advanced Metricsthe Thunder have allowed 11.8 more points per 100 possessions this season with Roberson on the bench. And when Roberson missed 10 games earlier this season, mostly with tendinitis in the patellar tendon he injured Saturday, Oklahoma City’s defense wasn’t the same. The Thunder allowed opponents to score 2.8 percent more efficiently than their usual offensive rating in those 10 games, as compared to holding them 3.2 percent below their typical efficiency with Roberson.

Opponent 3-point shooting might have inflated the difference Roberson makes to some extent. Teams shot 37.2 percent from 3-point range against the Thunder in the 10 games he missed, as compared to 35.3 percent in other games; and foes have generally shot better with Roberson on the bench — something that can’t be attributed to a single defender. Nonetheless, there’s ample reason to believe Roberson is one of the league’s top perimeter defenders. An NBA All-Defensive Second Team pick last season, Roberson made my first team.

Though Oklahoma City has another wing stopper in Paul GeorgeRoberson’s presence allowed the Thunder to take advantage of George’s ability to freelance defensively while guarding weaker opponents. George is averaging a career-high 3.0 steals per 100 opponent plays, which ranks fifth in the league. Expect that to decline now that George’s primary assignment will shift to defending the opponent’s best scorer. In the 10 games Roberson has missed, George’s steal rate has dropped to 2.3 per 100 plays.

Replacing Roberson in-house

Perhaps the biggest surprise about Oklahoma City’s performance without Roberson earlier this season is not so much that the defense suffered — that would be expected, given his pedigree, if perhaps not to the degree we’ve seen — as that the offense didn’t improve much.

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For all his ability at the defensive end, Roberson is one of the weakest offensive perimeter players in the NBA. He has made just eight 3-pointers in 36 attempts (22.2 percent) this season, meaning opposing defenses feel comfortable to leave him on the perimeter and help on the Thunder’s star players. Roberson’s poor foul shooting (29.7 percent on 37 attempts this season, 46.5 percent career) also made him vulnerable to intentional fouls at times.

So in theory, Oklahoma City should improve offensively to make up some of the defensive hit. Yet the difference has been marginal so far: The Thunder scored 1.8 percent more efficiently than the opponent’s typical defensive rating during the 10 games Roberson has missed, as compared to 1.3 percent better than usual with him in the lineup.

That partially reflects Oklahoma City’s inability to come up with a good alternative on the wing. Terrance Ferguson started the last seven games Roberson missed, and while the 19-year-old rookie showed promise while scoring a career-high 24 points in a blowout win over the Los Angeles Lakers on national TV, overall he shot just 39.5 percent from the field and 33.3 percent from 3-point range. Ferguson totaled just 10 points in the last five games he started, presenting opponents little more threat than Roberson has.

Meanwhile, second-year guard Alex Abrines — a better 3-point shooter at 38.3 percent this season — has lost his rotation spot to Ferguson because he has struggled with other facets of the game. Forward Josh Huestis offers the most similar skill set to that of Roberson, for better or worse. His length is useful on defense, but Huestis has shot 28.4 percent from downtown.

If the Thunder’s coaching staff knows Roberson will be out the remainder of the season, they might get more creative in replacing him. One option is to go bigger, moving Carmelo Anthony back to small forward — a position he has played for just 157 minutes all season, per NBAwowy.com — and using either Jerami Grant or Patrick Patterson at power forward. Because he can shoot and capably defend, Patterson is probably Oklahoma City’s best and most complete option alongside the starters. However, Anthony might not be capable of defending wings for extended periods at this point, which would make a big lineup a non-starter.

Could the Thunder deal for a replacement?

Once the news of Roberson’s initial diagnosis broke, ESPN’s Royce Young suggested it might change how Oklahoma City approaches the trade deadline. While acquiring a defender of Roberson’s ability isn’t realistic for the Thunder, they could at least add a more reliable shooter who would help space the floor for their stars.

Making a deal will be challenging for Oklahoma City. Adding salary in a deal would be particularly costly because the Thunder already are scheduled to pay more than $20 million in luxury taxes. And Oklahoma City also can’t trade a first-round pick until at earliest 2022 because of past deals.

The best strategy for the Thunder might be to target cheaper players in the final year of their contracts. Joe Harris of the Brooklyn Netsmaking $1.5 million, would be an ideal target. Or Oklahoma City could look to move Abrines as part of a deal for a slightly more expensive player, such as Marco Belinelli of the Atlanta Hawks.

The timing of Roberson’s injury is particularly tough for the Thunder, because the team had just started to come together at both ends after adding Anthony and George in offseason trades. Oklahoma City also is in a fight for playoff positioning, having climbed within a game of the Minnesota Timberwolves for home-court advantage in the first round of the playoffs and just two games back of the San Antonio Spurs for the third seed — crucial because it likely means avoiding a potential matchup with the Golden State Warriors in the second round.

The Thunder still have enough talent on hand to win a playoff series and be competitive deeper in the playoffs — provided they can find the right replacement for Roberson.